Fluoride glasses



Patented Apr. 5, 1949 FLUORIDE GLASSES Kuan-Han Sun and Thomas E.Callear, Rochestcr, N. Y., assignors to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey No Drawing. ApplicationApril 6, 1946, Serial No. 660,308

This invention relates to improved fluoride glass and particularly to aspecific embodiment of the invention generically claimed in theapplication of Kuan-Han Sun, one of the present inventors, and MauriceL. Huggins, Serial No. 568,314, filed December 15, 1945.

As pointed out in that application, a glass can be made entirely offluorides and among the many possibilities there pointed out arecombinations of the fluorides of aluminum and beryllium with those ofdivalent metals. This present specification is specific to a glassconsisting entirely or predominantly of the fluorides of magnesium,lead, aluminum, and beryllium. Glasses of such composition can be madein comparatively large batches.

Although in certain of the examples given in the above-mentionedapplication, lead fluoride is present in amounts up to 30 per cent byweight, we have found that it is possible to obtain useful glasseshaving a much greater proportion of lead, and at the same time, toreduce the amount of beryllium fluoride, a poor moisture-resisting andrelatively expensive ingredient, to much less than in any of theexamples given in that application.

Examples indicating the possible range of proportions will now be given,the letter W indicating Weight per cent, and M the mole per cent of theseveral ingredients. In Formulas 2, 3, and 4 the amount of berylliumfluoride is particularly low, but a certain minimum amount appears to benecessary.

While the examples given above contain only the four fluoridesmentioned, the introduction of small amounts of other compatiblefluorides, particularly those of calcium, strontium, barium, lanthanum,cerium, and thorium, is usually advantageous in improving the chemicaldurability and devitrification. The glasses have an index of refractionfor the D line well over 1.4.

In making these glasses, dry powdered materials are used. About 10 percent of ammonium fluoride (NH4F) or ammonium acid fluoride (NH4HF2) isusually added to the batch. The ingredients of the batch, except thelead fluoride, are mixed and melted down in a covered platinum 7 Claims.(Cl. 106-47) 2 crucible at a temperature between 850 and 900 C. to aclear liquid or a fused mass, and then the lead fluoride is added andheating continued. This procedure avoids the decomposition of the leadfluoride and the attacking of the platinum by free metallic lead. Bythis procedure, a platinum vessel can be safely used for melting thelead-containing glasses. The glass should be poured from the crucible assoon after the addition of the lead fluoride as a clear liquid isobtained. It may be poured out into a mold which may be cold or may beheated to a temperature of the order of 200 to 300 C.

Of these formulas, those having the larger percentages of lead fluorideand smaller amounts of beryllium are preferred, particularly Examples 3and 4; that is, those in which the amount of lead fluoride is greaterthan 70 per cent by weight, although it is in all cases greater than 50per cent, and in which beryllium fluoride is between 3 and 12 per centby weight or 1 and 25 mole per cent, and in any event less than 20 percent by weight. The total of the glass formers, aluminum and berylliumfluorides, is preferably between 40 and 50 mole per cent or 19 and 32per cent by Weight, although it may be as high as 37 per cent by weightor 60 mole per cent, as in Example 1. The amount of aluminum fluoridewill, resultantly, have the limits of and 20 per cent by weight and 20and mole per cent, and the amount of magnesium fluoride will be between2 and 15 per cent by weight and preferably less than 10 per cent.

Having thus described our invention, what we claim is:

1. Optical glass consisting predominantly of compatible fluorides andresulting from fusion of a batch of which beryllium fluoride constitutesbetween 10 and 25 mole per cent, and the total of aluminum and berylliumfluorides amounts to between and mole per cent.

2. Optical glass consisting predominantly of compatible fluorides andresulting from fusion of a batch of which beryllium fluoride constitutesfrom 3 to 12 per cent by weight, and the total of beryllium and aluminumfluorides amount to between 19 and 32 per cent by Weight.

3. Fluoride optical glass consisting of the compatible fluorides oflead, magnesium, beryllium, and aluminum.

4. Fluoride optical glass resulting from a batch consisting ofcompatible fluorides and containing by weight: lead fluoride, between 50and '75 per cent; magnesium fluoride, between 2 and 15 per cent;beryllium fluoride, between 3 and 20 per 3 cent; aluminum fluoride,between and 20 per cent.

5. Fluoride optical glass resulting from fusion of a batch consisting ofcompatible fluorides and containing by weight: lead fluoride, at least'70 per cent; magnesium fluoride, between 2 and 10 per cent; berylliumfluoride, between 3 and per cent; and aluminum fluoride, between 10 andper cent.

6. Fluoride optical glass resulting from fusion of a batch comprisingpredominantly the following fluorides present in the weight percentagesas given: lead fluoride, at least per cent; magnesium fluoride, between2 and 15 per cent; beryllium fluoride, between 3 and 20 per cent;aluminum fluoride, between 10 and 20 per cent; the total amount ofaluminum and beryllium fluorides being at least 19 per cent.

7. Fluoride optical glass resulting from fusion of a batch comprisingpredominantly the following fluorides present in the weight percentagesas given: lead fluoride, at least per cent; magnesium fluoride, between2 and 10 per cent: beryllium fluoride, between 3 and 15 per cent;aluminum fluoride, between 10 and 20 per cent; the total of aluminum andberyllium fluorides being between 19 and 25 per cent.

The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date Great Britain 1907 Number

